Field of the Invention
The present invention relates, in general, to fixtures and apparatus for holding workpieces during manufacturing operations and, more specifically, to fixtures and apparatus for holding workpieces during inspection, dimension checking or gaging operations.
In manufacturing operations, workpieces or parts are manufactured to prescribed dimensions and shape. For quality control purposes, manufactured parts are checked on a scheduled basis against a standard or master part or set of dimensions.
During such checking operations, the workpiece is mounted in a workpiece holder and its dimensions checked by hand using gages, etc., to determine its correlation to the desired dimensions or master part. Coordinate measuring machines (CMM) are also employed to electronically measure the dimensions of a part held in a holder and to compare such dimensions with an established standard.
In such checking or gaging operations, the workpiece holder is typically a dedicated fixture constructed for one particular part, workpiece or assembly. The holder is constructed of a frame mountable on a grid plate to establish known reference coordinates. Various clamps, locators, etc., are then mounted on the frame and hold the workpiece or part in a known location with respect to the reference coordinates while checking is performed via hand-held gages or a coordinate measuring machine.
The dedication of one fixture for each specific part is extremely costly since the entire fixture is typically discarded when the part is extensively changed or becomes obsolete. Further, the storage of such fixtures is a problem due to the large number of fixtures required in certain manufacturing operations. In an automobile assembly and/or stamping plant, the large number of different vehicles necessitates a correspondingly high number of fixtures, each requiring storage space when not in use.
The large number of dedicated fixtures also leads to lengthy setup times. Each fixture must be first removed from the checking station and returned to storage before the next fixture to be used is brought from storage and accurately located on the grid plate before checking can commence.
To overcome these problems, several attempts have been made to develop modular workpiece holder assemblies in which workpiece holders, such as clamps, locators, etc., are attached to a common base having an X-Y grid arrangement of mounting bores. The X-Y grid arrangement of mounting bores enables the workpiece holder elements to be mounted in any desired position on the base to hold any one of a different number of parts or workpieces for checking, with only the holder elements being specifically designed for each different workpiece.
However, lengthy setup time remains a problem with such modular workpiece holding fixtures as the location of the base and the attached clamps, locators, etc., must be precisely determined each time a different workpiece is to be checked. The dimensional accuracy of the locators or clamps attached to the base must also be ascertained during each setup.
Thus, it would be desirable to provide a workpiece holder which decreases the setup time required in positioning a checking fixture to check the dimensions of a manufactured part or workpiece. It would also be desirable to provide a workpiece holder which minimizes storage requirements of such holders in a manufacturing facility. It would also be desirable to provide a workpiece holder for checking the dimensions of a workpiece which includes reusable components to minimize cost, even when the part being checked changes or becomes obsolete. Finally, it would also be desirable to provide a workpiece holder which reproducably accurately locates a workpiece or part for a checking or gaging operation.